The present invention relates to a thin film magnetic head adapted for use with a magnetic drum, tape or disc equipment for an electronic computer system.
The thin film magnetic head of the kind mentioned above is realized by resorting to the thin film techniques for increasing the density of magnetic recording on the magnetic drum, magnetic tape and magnetic disc and usually composed of a lower magnetic film, an upper magnetic film cooperating with the lower magnetic film to constitute a magnetic circuit provided with a magnetic gap and a coil conductor film extending between the upper magnetic film and the lower magnetic film so as to intersect the magnetic circuit, these films being implemented in a laminate structure on a substrate with electrically insulating films being interposed at regions where they are required. In some applications, a portion or the whole of the substrate may be made of a magnetic material so as to serve also as the lower magnetic film.
As important problems to be solved in this type of the thin film magnetic head, the following two may be mentioned: (a) miniaturization of the thin film magnetic head and improvement on magnetic characteristics of the head such as reduction in energy or power required in write operation and increasing of sensitivity of the head in read operation; and (b) realization of the head structure with high precision through facilitated manufacturing processes.
One of methods of dealing with the two problems mentioned above resides in the use of a photo-sensitive resin for an electrically insulating layer which is interposed between the upper magnetic film and the lower magnetic film. According to this method, gaps formed between the individual turns of the coil constituted by the coil conductor film are filled with the resin material, as the result of which the upper surface of the insulating layer located above the coil conductor film is flattened without unevenness or roughness to thereby allow the upper magnetic film to be flately formed over the insulating layer. With this structure, permeability of the thin film magnetic head can be increased signficantly as compared with the magnetic head suffering the roughness. Further, the method mentioned above makes it unnecessary to use an etching mask in contrast to other methods which require the etching mask for performing the photoetching of the insulating film, whereby the insulating film can be formed with a high pattern precision or accuracy, reducing unevenness in precision among the products.
On the other hand, the insulating film or layer formed of the photo-sensitive resin suffers a shortcoming in that the high-temperature withstanding capability is poor as compared with the insulating layer formed of an inorganic material such as SiO.sub.2, Al.sub.2 O.sub.3 or the like and the one formed of a resin of polyimide resin series which exhibits a sufficiently high resistance to a high temperature. Thus, the method of forming the upper magnetic film on the insulating layer is disadvantageously restricted to the process in which any appreciable increasing in temperature is not encountered in forming the upper magnetic film. The reason may be explained as follows.
As a method of forming the magnetic film which is not accompanied with any substantial increase in temperature, a plating process may be mentioned. However, the plating method is disadvantageous in that composition of the magnetic film undergoes remarkable variations even when slight changes occur in the plating conditions, involving thus a great difficulty in manufacturing the magnetic film having desired magnetic characteristics with a satisfactory reproductivity. Besides, it is difficult to control the distribution of film thickness so that the magnetic film of a uniform thickness be obtained. Further, equipment for processing exhaust liquid resulted from the plating process has to be installed, to another disadvantage.
There may be conceived an evaporation process or a sputtering process for the other method which is capable of forming the magnetic film without giving rise to the increasing in temperature. However, when the upper magnetic film having a required thickness in a range of 1 .mu.m to 8 .mu.m is formed with the temperature of the substrate being held at a sufficiently low level so as not to exert any adverse influence to the insulating layer, then the magnetic film is converted to the film exhibiting a vertical magnetic anisotropy having an easy axis of magnetization in the thicknesswise direction of the film owing to an internal stress, whereby the permeability is remarkably reduced down to 300 or less. The magnetic head formed of this kind of the magnetic film requires an increased power for write operation while the sensitivity of the head in read operation is degraded to such a degree that the magnetic head can no more be used for practical applications.
As will be appreciated from the foregoing, the thin film magnetic head in which the light-sensitive resin is used as the insulating film or layer suffers many difficult problems which remain to be solved.